An arteriovenous malformation, which occurs most frequently in the brain or spine, is a tangle of abnormal blood vessels. In a normal vascular system, your heart sends oxygen-rich blood to your brain through arteries, which slow down blood flow by sending it through several smaller blood vessels, ending with the smallest blood vessels, called capillaries. The capillaries slowly deliver oxygen to the surrounding tissue through their very thin walls, which allow oxygen to escape.

From there, the now oxygen-depleted blood drains from the tissue through a reverse course back to your heart and lungs, which refuel it with oxygen. In an AVM, however, the arteries (oxygen-rich) and veins (oxygen-poor) are missing this network of progressively smaller vessels, causing blood to flow directly from your arteries to your veins, bypassing the surrounding tissues. This means that not only is the surrounding tissue not getting the oxygen it needs, but it also puts tremendous pressure on the surrounding blood vessels.

The first symptom of an AVM is usually aneurysm, although when it does present symptoms prior to an aneurysm, they can include seizures, muscle weakness or numbness, vision loss, confusion, and difficulty speaking. See a doctor immediately if any of these symptoms occur.

Surgical treatment options for an arteriovenous malformation include surgical removal and endovascular embolization, which involves injecting a clotting mechanism through a catheter into the affected artery to stop blood flow to the AVM.